Paper coating compositions typically contain binders, pigments, lubricants, defoamers, bactericides, fungicides and other additives depending on the desired end product. Starches such as natural starches, oxidized starches, enzyme converted starches or the like typically comprise the binder component which functions to bind the pigment particles together and to bind the coating layer to the raw stock. Other commonly used binders include proteins such as casein, water soluble polyvinyl alcohols, polyacrylamides, styrene-butadiene resins or the like. Where water penetration resistance is a prime requirement, an insolubilizer is added to the coating composition to crosslink the binder.
Glyoxal, a highly reactive dialdehyde, has been demonstrated to be an excellent binder insolubilizing agent. However, glyoxal is so reactive that it cannot be used as such and must be blocked to moderate its reactivity as described, for example, in U.S. Pat. Nos. 4,471,087 and 4,455,416. The '087 patent discloses an oligomer of glyoxal and urea and the '416 patent discloses a condensation product of glyoxal, cyclic urea and polyol.
Other glyoxal-urea reaction products said to be useful as binder insolubilizing agents are described in U.S. Pat. Nos. 3,869,296; 3,917,659; and 4,343,655.